1) Field of the Invention
The present invention relates to improvements in electrical discharge machining solutions of the aqueous solution type and also to improvements in electrical discharge machining processes which make use of an electrical discharge machining solution of the aqueous solution type. More specifically, the present invention provides rust inhibitors which have excellent rust preventive properties, are hardly adsorbed on ion-exchange resins and do not substantially lower the resistivities of electrical discharge machining solutions of the aqueous solution type. The present invention also provides aqueous-solution-type electrical discharge machining solutions which facilitate the control of high resistivity within a predetermined range and strongly inhibit the formation of rust on work pieces and machining equipment. The present invention further provides electrical discharge machining processes which can be stably practiced over a long time.
2) Description of the Related Art
Electrical discharge machining is a machining process for die-milling or die-sinking, boring or cutting an electrically conductive work piece by producing a spark discharge between a machining electrode and the work piece in an electrical discharge machining liquid or solution which is an insulating medium.
Conventionally, kerosene has been used primarily as such an electrical discharge machining liquid. Evaporation of kerosene is however unavoidable due to the generation of heat upon electrical discharge machining. Since kerosene is a highly flammable liquid, kerosene gas so evaporated and vaporized tends to catch a fire due to a spark or a pillar of arc produced upon electrical discharge. Kerosene therefore has the inherent drawback that it involves high fire hazards.
With a view toward avoiding the above-mentioned fire hazards, various techniques have been developed using the following non-flammable electrical discharge machining liquid or solutions.
(1) Pure water; PA0 (2) Aqueous solutions of polyhydric alcohols such as glycols and saccharides (for example, Japanese Patent Publication No. 16480/1966, Japanese Patent Publication No. 4253/1984 and Japanese Patent Application Laid-Open No. 108743/1981.); PA0 (3) Aqueous solutions of derivatives of polyhydric alcohols (for example, Japanese Patent Application Laid-Open No. 107844/1981, Japanese Patent Application Laid-Open No. 94223/1987, Japanese Patent Application Laid-Open No. 2614/1978 and Japanese Patent Application Laid-Open No. 2615/1988.); PA0 (4) Aqueous solutions of polyethers (for example, Japanese Patent Laid-Open No. 4623/1986, Japanese Patent Laid-Open No. 181828/1987, Japanese Patent Laid-Open No. 236623/1987, Japanese Patent Laid-Open No. 236624/1987 and Japanese Patent Laid-Open No. 2617/1988.); and PA0 (5) Mixtures of two or more of the above non-inflammable electrical discharge machining liquid and solutions (1)-(4).